Thermal and hydrodynamic CFD evaluation of throat sizing effect on biomass gasification performance in downdraft fixed-bed reactor

Abstract

Throated downdraft gasifiers have the high tendency to pressure drop that hinders the smooth operations of these reactors. The ratio of gasifier throat diameter to gasifier diameter has an unprecedented impact on the pressure drop of downdraft reactors. The main aim of this study is to investigate the effect of reducing the throat on pressure, velocity, turbulence, and temperature in the reduction and oxidizing zones of the gasifier through computational fluid dynamics. The recorded data indicated a significant increase in both turbulence and velocity by 16% and 21% respectively, while there was a marginal increase in the pressure drop when T_R0.12 and T_R0.40 models were compared. The gasification temperature tremendously improved as the throat ratio is decreased from 0.40 to 0.12. Additionally, the gasifier performance in terms of carbon conversion, cold gas, gasification efficiencies as well as heating values are also dealt with. The results show that lower throat ratios increase the carbon conversion, heating value, and cold gas efficiency of the process to the tune of 8.61%, 15.3%, and 8.58% respectively when the T_0.12 and T_R0.40 were compared.